title: New strategies to overcome resistance to mammalian target of rapamycin inhibitors in breast cancer.
abstract: OBJECTIVE
  To review the studies addressing mammalian target of rapamycin (mTOR) inhibitors in breast cancer and resistance to rapalogs. Preclinical and clinical studies have suggested mTOR inhibitors may help overcome the resistance to endocrine therapy and trastuzumab. Despite much interest, knowledge of the mechanism and molecular response to mTOR inhibitors is incomplete.
  
  
  RESULTS
  Resistance to mTOR inhibitors has been explored in preclinical studies and can be defined as primary, associated with amplifications or mutations of different kinases, or secondary, in which rapalog activates the feedback loops involving the insulin-like growth factor I receptor (IGF-IR), platelet-derived growth factor receptor and mitogen-activated protein kinase (MAPK) pathway. Current clinical trials are testing the combinations of rapamycin with other kinase inhibitors including IGF-IR, phosphoinositide 3-kinase and MAPK-extracellular signal-regulated kinase inhibitors.
  
  
  CONCLUSIONS
  Recent findings on the resistance to rapalogs have stimulated the assessment of combinations of inhibitors in clinical trials. This review summarizes the current knowledge of primary and secondary rapalog resistance, and the current efforts to overcome this resistance.
authors.affiliation: aInstitut National de la Santé et de la Recherche Médicale (INSERM) U981 bDepartment of Medical Oncology, Gustave Roussy Institute (IGR), Villejuif, France.
authors.forename: Cecile
authors.initials: C
authors.lastname: Vicier
authors.forename: Maria V
authors.initials: MV
authors.lastname: Dieci
authors.forename: Fabrice
authors.initials: F
authors.lastname: Andre
mesh_terms: D000730:Androstadienes / Q000008:administration & dosage; D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D014408:Biomarkers, Tumor / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology; D002986:Clinical Trials as Topic; D004359:Drug Therapy, Combination; D000068338:Everolimus; D005260:Female; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects*; D058990:Molecular Targeted Therapy / Q000379:methods*; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage*; D017526:Receptor, IGF Type 1 / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000008:administration & dosage / Q000031:analogs & derivatives; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000068878:Trastuzumab; D016896:Treatment Outcome
chemical_list: D000730:Androstadienes; D061067:Antibodies, Monoclonal, Humanized; D014408:Biomarkers, Tumor; D047428:Protein Kinase Inhibitors; D000068338:Everolimus; C546842:MTOR protein, human; D017526:Receptor, IGF Type 1; D058570:TOR Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; C056516:exemestane; D000068878:Trastuzumab; D020123:Sirolimus